1. Field of the Invention
The present invention generally relates to apparatus and methods for continuous monitoring of health condition in patients with congestive heart failure.
2. Background Information
Congestive heart failure (xe2x80x9cCHFxe2x80x9d) is a chronic inability of the heart to maintain an adequate output of blood from one or both ventricles of the heart to meet the metabolic demands of the tissues. With a markedly weakened left ventricle or right ventricle or both, the volume of blood presented to the heart is in excess of the heart""s capacity to move it along. Consequently, fluid builds up behind the heart. With a weakened left ventricle or right ventricle or both, there is a shift of large volumes of blood from the systemic circulation into the pulmonary (lung) circulation. If the inability to move the volume of blood forward is due to a left heart problem without the right side failing as well, blood continues to be pumped into the lungs by the normal right heart, while it is not pumped adequately out of the lungs by the left heart. As the volume of blood in the lungs increases, the pulmonary vessels enlarge, pulmonary venous congestion develops, and, once the pulmonary capillary pressure rises above a critical point, fluid begins to filter out of the capillaries into the interstitial spaces and alveoli (air sacs in the lungs where exchange of oxygen and carbon dioxide occurs), resulting in pulmonary edema. Subsequently this can lead to pleural effusion (effusion is the escape of fluid into a part) and abdominal effusion. If the abnormality lies in the right heart or the pulmonary arteries, limiting the ability to move blood forward, then congestion occurs behind the right heart (causing pleural effusion and/or build up of fluid in the abdomen).
CHF is the fourth leading cause of death in the United States and a leading cause of poor quality of life in the population over 65. There are 5 million cases of CHF in the United States. In patients diagnosed with CHF, sudden cardiac death occurs at 6 to 9 times the rate of the general population. A 44 year follow-up Framingham Heart Study of the National Heart, Lung and Blood Institute (the xe2x80x9cNHLBIxe2x80x9d, part of the U.S. National Institute of Health), has found, based on hospital admissions, that there are nearly 550,000 admissions of new cases of CHF each year in the United States. The number of patients hospitalized for CHF annually is 1.01 million. CHF approaches 10 cases per 1000 members of the U.S. population after age 65. CHF hospitalizations have increased steeply in the last 20 years, the number of hospital discharges (which includes both the living and the dead) more than doubling both for males and females from 1979 to 1999. As the population of 65 and older grows hugely in the U.S. with the aging of the baby boomer generation, and as the number of first heart attack survivors increases, CHF portends a dramatic increase of morbidity and mortality and a burgeoning drain on healthcare funds in the U.S.
One of many needs for CHF patients is accurately predicting when they have a significantly worsening condition signifying death draws near. With sufficient warning, steps can be taken to save them. Among CHF patients in the very poorest condition, there is a need to know which patients are likely to have the shortest lives in order to select those for whom heart transplantation or left ventricular assist device (LVAD) implantation is the appropriate treatment.
Bedside classifiers such as age, sex, ischemic heart disease (IHD), cardiac cachexia, and New York Heart Association (NYHA) functional classes for CHF are useful factors for general prognosis of risk of poor outcome, but do not provide physiologically specific or dynamic information. With today""s sophisticated medical diagnostics technology, especially in large urban medical center complexes, much can be done in a hospital environment to develop specific test information concerning the condition of a patient""s heart. Numerous predictors of mortality in patients with CHF have been described in the literature. Some of the tests that can be performed include, without limitation: chest wall impedance, chest impedance peak oxygen uptake (dot(V)O2), left and right ventricular ejection function (LVEF and RVEF), both respiratory and circulatory response to exercise (exercise capacity, especially if combined with maximal oxygen consumption), cardiac index, left ventricular cavity size, left ventricular stroke work index, right and left ventricular filling pressure (RVFP and LVFP) and isovolumic relaxation time (LV IVRT), left ventricular systolic pressure (LV SP), right and left atrial pressure, systemic vascular resistance, calculated wall stress, tricuspid regurgitation (TR), jugular venous pressure (JVP), pulmonary capillary wedge pressure (PCWP), 6-minute walk distance, arterial and venous pH, pO2, pCO2, serum creatinine, serum sodium, plasma norepinephrine, plasma neurotensin, plasma renin activity (PRA), plasma arginine vasopressin, plasma atrial and brain natriuretic peptides, plasma endothelin-1, plasma interleukin-6, plasma tumor necrosis-alpha, serum sodium, serum potassium (and total potassium stores), serum magnesium, lymphocyte count, frequent ventricular extrasystoles, ventricular tachycardia (VT), bundle-branch blockage (left and right), atrial fibrillation or flutter, T-wave alternans, QT prolongation and dispersion, PACO2, pH, respiratory rate, QRS width, Rxe2x80x94R variability, and dP/dt. Quite surprisingly, however, these heart performance or heart condition factors together account for only a portion of statistical variance as a predictor of poor outcome in CHF patients, usually applying to only a few patients, leaving prognosis uncertain for the individual patient.
Even these tests don""t help much if the patient isn""t hospitalized to receive them at a critical time. Home-monitoring promises an opportunity to reduce costs and improve quality of life in some patients. Prognostic variables described in the literature that might be readily monitored at home include S3 gallop, Cheyne-Stokes respiration, apnea/hypopnea index, systolic blood pressure (SBP), heart rate at rest (HR), pulse pressure (PP), and mean arterial pressure (MAP). However, these factors are not statistically strong predictors of risk of imminent death.
Our invention involves detecting a significant worsening of condition of a CHF patient and issuing an alert so that life saving therapies and interventions can be summoned to save the patient""s life and/or intervention devices can be activated or adjusted. In an aspect of the invention, the output of an alert is to a medical device that applies a therapeutic treatment to the patient to treat the patient""s condition of congestive heart failure. The device suitably may be a ventricular assist device responsive to the alert to provide additional ventricular assist to the patient. The device may be an medication release device responsive to the alert to adjust the amount of medication the patient is receiving. Or the device may be a cardiac rhythmic regulator, such as a pacemaker or defibrillator, responsive to the alert to optimize the patient""s regulator parameters to reverse hypothermia, or a device responsive to the alert to warm the patient.
In a significant departure from use of other prognostic factors, these new methods and apparatus not only are dynamically predictive but also are applicable for watching the individual patient on an ambulatory and continuous basis, allowing the patient to be monitored at home or elsewhere as well as in-hospital. This allows the patient an improved quality of life yet protects the patient by enabling immediate availability of professional care appropriate to his or her condition for timely initiated therapy or intervention.
In the parent application of which this is a continuation in part, there is described the discovery that very mild hypothermia is an indicator of imminent death in CHF patients. Hypothermia is generally defined as a core body temperature of 35xc2x0 C. (95xc2x0 F.) or below and is classified as mild (35-32xc2x0 C.; 95-89.2xc2x0 F.), moderate ( less than 32 to 28xc2x0 C.;  less than 89.2-82.4xc2x0 F.), or severe ( less than 28xc2x0 C.;  less than 82.4xc2x0 F.). See Petty, K. J., xe2x80x9cHypothermiaxe2x80x9d, in CARDINAL MANIFESTATIONS AND PRESENTATION OF DISEASES, McGraw-Hill Companies, 1998.
In continuing this investigation, we have now discovered that rate of fall of temperature of a CHF patient varies insignificantly compared to single temperature measurements at admission or at any time during hospitalization, and that, accordingly, rate of temperature fall provides a primary and sensitive measure for prediction of imminent death that can prompt issuance of an alert for life saving steps to be timely initiated.
In accordance with our discovery, our invention includes methods, means, apparatus and systems for continuously monitoring a CHF patient against a cut-off point set for rate of fall of body temperature as at least one temperature attribute of the very mild hypothermia that is an indicator of imminent death in CHF patients.
The method, means, apparatus and systems alert a worsening of condition in a patient with congestive heart failure, in operations which comprise (a) pre-setting a cut-off point of at least one temperature attribute of hypothermia comprising rate of fall of body temperature relative to optimum sensitivity and specificity for such attribute as a congestive heart failure predictor of death of a patient, (b) routinely determining that attribute in the patient, (c) determining from the routine determinations of the attribute whether a condition of congestive heart failure hypothermia has occurred, and if so, (d) issuing an alert warning of the worsening condition.
In one aspect operation, (c) comprises determining whether the attribute has attained or crossed the cut-off point. In another aspect in which the invention comprises routinely determining the attribute for at least one peripheral site and for a core site, operation (c) comprises determining whether the attributes in both the sites are moving in the direction of the cut-off point. In another aspect, operation (c) comprises determining whether rise of core temperature of the patient from a temperature below a baseline temperature of the patient to a temperature at or closer to baseline lags behind rise of core temperature of the normal person from a temperature below a baseline temperature of the normal person to a temperature at or closer to baseline, or if the core temperature of the patient rises from a temperature below a baseline temperature of the patient to less than a predetermined minimum acceptable rise.
In an embodiment of our invention, the cut-off point is set relative to optimum sensitivity and specificity for rate of fall of body temperature as at least one temperature attribute of hypothermia as a congestive heart failure predictor of death of a patient. That attribute is periodically determined in the patient, and that attribute is reckoned for whether it has attained or crossed the cut-off point set for that attribute, and if so, an alert is issued.
In addition to at least rate of fall of body temperature as one temperature attribute of hypothermia as a congestive heart failure predictor of death of a patient, the attribute also may be a hypothermic body temperature of the patient, amount of body temperature fall in a selected interval, the interval""s duration, and the frequency of such intervals.
By setting the cut-off point relative to optimum sensitivity and specificity for rate of fall of body temperature, the invention enables customizes the alarming system toward the specific health condition and needs of the patient. The system alarms sooner if the patient is in an otherwise poorer prognostic category, suffers other mental/health disabilities, or is located away from healthcare. This presetting, which is done by the health care professional that oversees the functionality of the device, or which in certain instances may be increased automatically, is based on (1) the patient""s other co-morbidities; (2) other prognostic factors; and (3) the time and distance availability of professional and/or nonprofessional healthcare.
Our invention also includes, in additional aspects and embodiments, personalization to the CHF patient""s own baseline temperature set-point, and personalization also to circadian and lunar changes in temperature of the patient. In another enhancement, the invention further comprises determining and making adjustments to periodically determined temperature attributes to take into account external factors, such as one or more environmental factors to which the patient is exposed, for example, temperature and light, and to take into account internal factors such as the patient""s activity, medications, smoking, alcohol use, or other factors that can affect the patient""s body temperature, such as hot or cold solid and/or fluid intake.
Another embodiment of our invention involves routinely determining a temperature attribute for at least one peripheral site and for a core site and determining whether that attribute in both such sites is moving in the direction of the cut-off point, and if so, outputting an alert. Temperature is measured both on the surface of the patient and at a location providing a core temperature, and watch is made for both low or falling core temperatures and low or falling surface temperatures (or both low and failing surface and core temperatures). Occurrence of a low or falling surface temperature at a time when baseline temperature stays normal may signify nothing more than exposure to a cold environment; or the patient""s having Raynaud""s disease, a condition in which peripheral circulation is impaired in the extremities. However, occurrence of low or falling surface temperatures coupled with low or falling core temperature is an ominous indication that heat is transferring from the core to the exterior surface where coldness indicates it is being lost with terminal consequences.
In another embodiment there is provided method and means for monitoring and warning of worsening of condition of congestive heart failure in a patient, which comprises monitoring and recording environmental temperature and core temperature of the patient and determining whether a steep fall in environmental temperature has occurred. If so, the patient""s core temperature and the patient""s change in core temperature over time is compared to a core temperature and a change in core temperature over time of a normal person at environmental temperatures monitored beginning with the temperatures included in the steep fall. An alert is issued if rise of core temperature of the patient, from a temperature below a baseline temperature of the patient to a temperature at or closer to baseline, lags behind rise of core temperature of the normal person from a temperature below a baseline temperature of the normal person to a temperature at or closer to baseline. An alert is alternatively issued if the core temperature of the patient rises from a temperature below a baseline temperature of the patient to less than a predetermined minimum acceptable rise.
These and numerous other aspects of our invention are described in detail below, including with reference in part to illustrations that are now described.